A HEV (Hybrid Electrical Vehicle) includes a motor and an internal combustion engine, and runs based on a driving force of the motor and/or the internal combustion engine depending upon the driving conditions of the vehicle. HEVs are divided roughly into two system types; a series system and a parallel system. A series system HEV runs based on power of the motor. The internal combustion engine is used to generate electrical power. The electrical power generated in a generator by means of power of the internal combustion engine is used to charge a battery or supplied to the motor. A parallel system HEV runs based on a driving force of either or both of the motor and the internal combustion engine. A series/parallel system HEV is also known in which both the systems are combined. In the series/parallel system HEV, a clutch is released or applied (disengaged or engaged) according to the driving conditions of the vehicle, whereby a transmission system of driving force is switched to either the series system or the parallel system.
In the HEV, in order to obtain a braking force that corresponds to a braking force obtained by an engine brake, regenerative braking is used in which the motor is caused to function as a generator while the vehicle is being decelerated. Regenerated energy that is obtained during the regenerative braking is generated for a braking force that is needed by the vehicle that is running, and therefore, it is not possible to control the amount of regenerated energy. Although the regenerated energy is used to charge the battery, the battery that is fully charged cannot absorb the regenerated energy.
FIG. 20 is a block diagram of a regenerated energy absorbing system of a hybrid vehicle described in patent literature 1. In the regenerated energy absorbing system shown in FIG. 20, an electronic control unit 4 detects that regenerative braking is activated from a signal sent from a brake switch 9. Then, when the regenerative braking is in operation, an inverter 6 is controlled so that regenerated energy generated in a motor 7 is used to charge a battery 5. However, in the case a voltage of the battery 5 is detected by a voltmeter 12 to be found that the voltage detected is equal to or larger than a predetermined value, the supply of fuel to an engine 1 is stopped, and the inverter 6 is activated so that a generator 2 is activated to operate as a motor that rotates the engine 1 as a load by means of the regenerated energy to thereby absorb the regenerated energy.